Sunday, 1 June 2014

Sony Ericsson MMR-70 Modding (Extreme this time)

Last year I posted simple LED mod for MMR-70 FM Transmitter. This time it is a bit more exterme as it includes rewriting firmware for onboard ATmega32L microprocessor.

This is how the end result looks like:

In addition to voltage, audio and I2C all ATmega32 pins needed for uploading firmware are exposed as test points. Schematics of MMR-70 can be fount here, applying it to the board:

Serial RX/TX is combined to a single test point 14, but by removing Schottky diode D1 (red crossed) and soldering wires direclty to contacts marked TX and RX we can use it with standard USB to TTL serial adapter.

None of analogue inputs of ATmega32L is populted, but again, using thin wires, thin soldering iron tip and thick nerves we can make them available.

OK, and now to something completelly different - to software. Let's make some use of digital PB0 and PB1 pins, connect relative humidity and temperature RHT03 sensor and write new firmware which will poll RHT03 and broadcast temperature and humidity values as RDS text: